Hence "to avoid busy-waiting." Some applications with softer low-latency requirements tend to spin for a certain amount of time before going to sleep and await

Hence "to avoid busy-waiting." Some applications with softer low-latency requirements tend to spin for a certain amount of time before going to sleep and await data arrival. Also, if it is hit with a constant stream of data to process, it wouldn't even get a chance to block. At the other extreme end of RT computing, you usually don't have an OS that blocks using privileged instructions in the first place. You just...schedule things.